238 INDUCTION. 



These three sets of instances admit of being treated according to the 

 Method of Agreement. lu all of them the metallic compounds are 

 broii"-ht into contact with the substances which compose the human or 

 animal body ; and the instances do not seem to agree in any other cir- 

 cumstance. The remaining antecedents are as different, and even 

 opposite, as they could possibly be made ; for in some the animal sub- 

 stances exposed to the action of the poisons- are in a state of life, in 

 others only in a state of organization, in others not even in that. And 

 what is the result which follows in all the cases ? The conversion of 

 the animal substance (by combination with the poison) into a chemical 

 compound, held togetlier by so powerful a force as to resist the subse- 

 quent action of the- ordinary causes of decomposition. Now organic 

 lif(3 (the necessary condition of sensitive life) consisting in a- contlhiial 

 state of decomposition and recomposition of the different organs and 

 tissues ; whatever incapacitates them for this decomposition desti-oys 

 life. And thus the proximate cause of the death produced by this, 

 description of poisons, is ascertained, as far as the Method of Agree- 

 ment can ascertain it. 



Let us now bring our conclusion to the test of the Method of Differ- 

 ence. Setting out from the cases already mentioned, in which the antece- 

 dent is, the presence of substances forming with the tissues a compound 

 incapable of putrefaction (and u fortiori incapable of the chemical 

 actions which constitute life), and the consequent is death, either of 

 the whole organism, or of some portion of it ; let us compare with these 

 cases other cases, as much resembling them as possible, but in which 

 that effect is not produced. And, first of all, " many insolnble basic 

 salts of arsenious acid are known not to be poisonous. The substance 

 called alkargen, discovered by Bunsen, which contains a veiy large 

 quantity of arsenic, and approaches very closely in composition to the 

 organic arsenious compounds found in the body, has not the slightest 

 injurious action upon the organism." Now when these substances are 

 brought into contact with the tissues in any way, they do not combine 

 with them ; they do not aixest their progi'ess to decomposition. As far, 

 therefore, as these instances go, it appears that ^^-hen the effect is 

 absent, it is by reason of the absence of that antecedent which we had 

 already good gi'ound for considering as the proximate cause. 



But the rigorous conditions of the Method of Difference are not yet 

 satisfied ; for we cannot be sure that these unpoisonous bodies agree 

 with the poisonous substances in every property, except the particular 

 one, of entering into a difficultly decomposable compound with the 

 animal tissues. To render the method strictly applicable, we need an 

 instance, not of a different substance, but of one of the vei-y same sub- 

 stances, under cu'cumstances which would prevent it from forming, 

 with the tissues, the sort of compound in question ; and then, if death 

 does not follow, our case is made out. Now such instances are afforded 

 by the antidotes to these poisons. For example, in case of poisoning 

 by. arsenious acid, if hydrated peroxide of iron is administered, the 

 destructive agency is instantly checked. Now this peroxide is known 

 to combine with the acid, and foi-m a compound, which, being in- 

 soluble, cannot act at all on animal tissues. So, again, sugar is 

 a well-known antidote to poisoning by salts of copper; and sugar 

 reduces those salts either into metallic copper, or into the red sub- 

 oxide, neither of which enters into combination with animal matter. 



